Many bad things happening in the environment can frequently be connected, directly or indirectly, to climate change. This is not one of those things. According to the story (you can read it too, including the video), a large school of menhaden (the very valuable filter-feeder fish that is an important middle trophic step in the oceanic and estuarine food chain) got cornered by hunting bluefish into the Shinnecock Canal on Long Island. Unfortunately, the locks on the canal were closed for the night. With all of the fish in a restricted water mass (I guess they were too agitated to swim back out), they rapidly used up the oxygen and died.
Too bad this mass can't get turned into fish protein, which is what menhaden is used for elsewhere -- like the Chesapeake Bay.